| Summary: | 碩士 === 國立中山大學 === 機械與機電工程學系研究所 === 94 === For the evaluation of non-ferrous heat exchanger tube, there are many non-destructive testing methods; however, the eddy current testing (ECT) method is the most popular one. By using of ECT, you may find out the defects existing inside or outside the tube wall, diagnose the heat exchanger system and find out the latent problems. The problem is that an improper signal analysis will result in error in the range of 15〜25% of the tube wall thickness, or even over 40% error. This is a great discouragement to the ECT inspectors, and will reduce the confidence of the proprietors of power plants or petro-chemical industries to the use of ECT. Therefore, in this thesis, the study is mainly focus on the problems of the aluminum brass tubes in condenser using ECT method. This thesis will analyze the causes of error of aluminum brass tubes when using ECT, prepare calibration and reference tubes, and test them using eddy current instruments. The relationship among the raw data with volts, phase angle and depth has been found. Two data evaluation methods are developed, one is the defect depth modification equation and the other is the auxiliary evaluation curve. The new methods are proved to be more accurate and practical in the evaluation of heat exchanger tube after more than one year of verification by field testing in the power plant. The results obtained in this thesis are very helpful to reduce the probability of tube failure.
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